1. Field of the invention
The present invention relates, in general, to compressing apparatus. More specifically, the invention relates to a scroll type compressing apparatus wherein a variable compressing space is defined between a stationary scroll member and a movable scroll member for compressing a gaseous fluid.
2. Description of the prior art
As is well known, a scroll type compressor typically includes a stationary scroll member and a movable scroll member. Each scroll member has a spiral wrap of involute or the like configuration. The stationary scroll member and the movable scroll member are arranged to oppose one another such that one end of sprial each wrap is in contact with the surface of the opposing scroll member. As the movable scroll member moves, the volume of a crescent shaped compressing shape defined by the pair of spiral wraps is reduced to carry out the compressing operation for a gaseous fluid such as, e.g., refrigerant, sealed in the compressing space.
As shown in FIG. 1, in such a compressor described above, each wrap 11, 13 of a stationary scroll member 15 and a movable scroll member 17 is formed in the involute curve, as described above, and each end portion of wraps 11 and 13 also is formed in the combination of the involute curved wall surface and an arcuate wall surface. The inner surface of each end portion of wraps 11 and 13 is formed on an arc-shape, which has a relatively large diameter extending to the outside of the locus of the involute of the remaining portion of the wrap 11, 13. Therefore, the thickness of each end portion of wraps 11 and 13 decreases, and the stress against each end portion increases when operating, resulting in decrease in strength of wraps 11 and 13. Cracks may occur during an extended use.
To avoid such undesirable cracks described above, an improved scroll type fluid compressor described in U.S. Pat. No. 4,547,137 issued to Terauchi et al. has thickened spiral elements. In this prior art, the inner edge portion of each spiral element or the inner middle portion of each spiral element exposed to the inner-most fluid pocket is thickened toward the inner-most fluid pocket. This prior art scroll compressor may avoid cracks, and may also minimize re-expansion of the compressed fluid. However, it may cause an excessive compression of the fluid due to the minimized fluid pocket, resulting in an increase in the power consumption.